Touch screens are capable of measuring touch position for a single touched point. Current touch screens are unable to effectively determine the position of touches by multiple users, discriminate among touches by multiple users, or enable the touch of one user while disabling the touch of another, especially when simultaneous touch down occurs. A number of touch screen applications would benefit from the ability to determine the position of multiple touches to a touch screen, discriminate among touches by multiple users and to enable touches by one user and not another.
Infrared and surface acoustic wave touch screen systems have the ability to locate two separate simultaneous touches in two of four possible locations, but they are unable to resolve the locations uniquely due to “shadow” effect. A capacitive touch system with the ability to discriminate between human touch and the simultaneous use of an inanimate object (a stylus) is disclosed in U.S. Pat. No. 5,365,461 by Stein et al. The system is an improvement of the definite capacitive disclosures in U.S. Pat. Nos. 4,371,746, 4,293,734, 4,198,539, and 4,071,691 to Pepper, Jr. These capacitive systems lack the ability to measure coordinates of two simultaneous human touches because the current flowing through the touch screen from each touch are combined, and the measured result indicates an average of two touch locations. A touch system addressing disadvantages of known touch systems and their components would be an important advance in the art.